A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle of a user is equipped with a navigation function to guide the user to a destination. Such a navigation system detects the current position of the user or user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a map data storage medium, for example, a hard disk or a DVD. The navigation system displays a map image on a monitor screen while superimposing a mark representing the current location of the user and the route to the destination thereon.
When a destination is set, the navigation system starts a route guidance function for setting a guided route from the start point to the destination. To determine the guided route to the destination, the navigation system calculates and determines an optimum route to the destination based on various parameters. For example, the guided route is determined based on the shortest way to reach the destination, the quickest way to reach the destination, the route preferring freeways to surface roads, the least expensive way to the destination, the route without using toll road, or the like.
Typically, a navigation system can display a map image with several icons. Such icons have various shapes and colors to represent corresponding objects such as types of points of interest (POI), a destination point, traffic incidents, freeway exits, etc. As is well known in the art, the recent map data used in a navigation system includes information on a large number of points of interest (POI), such as restaurants, shops, gas stations, etc. Thus, a large number of icons will be displayed on a small area of map image when displaying a map image of an area condensed with POIs, such as a downtown or commercial areas such as shopping malls. For the user can easily observe on the monitor screen, the sizes of such icons must not be too small.
Accordingly, in many cases, many icons are displayed on the map image to provide sufficient information to the user. Typically, the user can change the scale of the map by zooming in or zooming out the map image to know the surrounding situation better. By zooming in, the user can see more details of a smaller area. By zooming out, the user can see a wider area with less detail. Thus, depending on the user's needs, the map scale is frequently changed by means of a remote controller, a touch screen, etc.
FIG. 1 is a display example in a conventional navigation system showing a map image with several icons. A display 51 contains a map image having several roads and other information. A cursor 61 is typically positioned at the center of the display screen. A destination icon 71a, point of interest icons 71b-71f, and traffic incident icons 71g and 71h are shown on the map image. A scale indicator 53 at the lower left indicates the current scale of the map image. In this display example, the scale of the map is ⅛ miles per unit length.
When the user zooms in the map image, the navigation system will display a magnified view of the map image. Such an example is shown in the display example in FIG. 2. As shown in the map scale indicator 53, the map scale is changed to 1/32 miles per unit length so as to enlarge the map image. When zooming in or out in this manner, typically, the navigation system magnifies or shrinks the map image while keeps positioning the cursor 61 at the center. In other words, the map image is either enlarged or shrunken with respect to the cursor point.
When enlarging the map image at the cursor point 61 as in the example shown in FIG. 2, the icons 71a and 71d-71f and 71h shown in FIG. 1 are not displayed on the screen of FIG. 2 because these icons are outside of the display area. In many cases, the user wishes to zoom in an area with respect to a certain incident or place that is most relevant to the user's situation. For example, in enlarging the map image of FIG. 1 to the one in FIG. 2, the user often wants to see the details around the destination 71b to know the shops and restaurants close to the destination or details of road structures close to the destination. However, as shown in FIG. 2, the destination icon 71a is not displayed, because the destination icon 71a is away from the center of the cursor 61 when the zoom in rate (rate of map scale change) is large.
Thus, there is a need to provide a navigation system that can rearrange a map image upon user's preference to zoom in or zoom out by taking the relevancy of objects for the user into consideration and adjusting the position of the object to the center of the cursor.